This invention relates to well casing support systems for suspending oilwell casings from a surface wellhead, and more particularly to split annular compression seals for use with a slip hanger forming a seal between a well casing and an inner surface of a casing head.
Prior known compression seals form a seal when an annular elastomer seal is compressed within the slip hanger structure. This type of seal is typically compressed between two or more relatively displaceable annular slip hanger components. The seal is typically formed with through holes for receiving pins or bolts that guide or draw together the slip hanger components. When the slip hanger components are displaced toward each other axially, the annular compression seal is deformed along a radial plane to engage the casing and the inner surface of the casing head.
Problems have occurred with these types of seals under broad temperature ranges because of the difficulty in controlling elastomer extrusion through the gaps that are necessary due to the manufacturing tolerances of the casing wellhead and hanger components. Furthermore, the thermal expansion and contraction of elastomer seal elements encased in the steel elements of hangers increase the difficulty in sealing due to amplification of stress in the elastomer. This results because the coefficient of thermal expansion of elastomers is about ten times greater than steel. With continuing development of the petroleum industry in increasingly severe environments, the requirements for safely controlling downhole pressures communicated to the surface of oilwells continue to become more demanding. Problems have occurred in these types of seals when the seals are extruded so that the diameters of through holes for receiving pins or bolts have a greater diameter than that of the pins or bolts, causing gaps in the seal. Similarly, gaps occur at inner and outer contact surfaces and at splits in between components adjacent the seal element.
Prior attempts to solve this problem included molding fabric or cord into the elastomer seal. This method has proven to have very limited capability at higher elastomer pressures. Another prior attempt to solve this problem, illustrated in FIG.5, has included the use of low modulus material and split extrusion washers 22 placed in a conical countersink 23 beneath a non-extrusion plate 21 adjacent the pins or bolts 12' as shown in FIG. 5. This method creates the need for many additional parts, especially if many load bolts or pins are required to pass through the seal element. Such a solution adds to cost and increased probability of assembly errors.